A report on United States Air Force C-123B assault transport aircraft performance in engineering and field assault condition test in Hagerstown, Maryland. A C-123B taxis and takes a right turn at Fairchild plant. Pylon tank or external fuel tank mounted under a wing of the C-123B. It takes off and in flight. The aircraft releases the pylon tank from the wing. The C-123B drops one of the main cell tanks from a 40' altitude past the runway and lands on grass beyond.